Biology · The Living World · NEET
A defining property is a feature that is TRUE for every living thing and FALSE for every non-living thing. So it works as a perfect test. Metabolism passes this test: every living organism (from a bacterium to you) shows metabolism, and no non-living object (a stone, a car) shows it. That is why NCERT calls metabolism a defining property of living organisms.
Because growth and reproduction have exceptions. Non-living things like mountains, sand dunes, and crystals also 'grow' (by adding material from outside). And many living things, like sterile worker bees, mules, or a person who never has children, do not reproduce, yet they are fully alive. Metabolism has NO such exception - all living things do it, no non-living thing does it. So it is the only feature with a perfect 'yes for life, no for non-life' record.
Yes. Scientists can take an enzyme out of a cell and make it run its reaction inside a test tube (called 'in vitro'). These isolated reactions are neither living nor non-living reactions - they still happen. But this is important: an isolated metabolic reaction in a test tube is NOT life. Life is the SUM TOTAL of all these thousands of reactions happening together in an organised way inside a cell. One reaction in a tube is a chemical event, not a living thing.
Yes. A dead body still has cells, proteins, and DNA, but its metabolism has STOPPED. Because the chemical reactions no longer run, it is non-living. This shows metabolism is the true marker of life - not just having cells or chemicals, but those chemicals actively reacting.
NCERT gives a second, deeper answer for the whole individual: consciousness - the ability to sense the environment and respond to stimuli. Metabolism is the defining feature at the level of cells and chemistry. Consciousness (self-awareness / response to stimuli) is described as the defining property at the level of the whole living organism. For NEET, remember BOTH: metabolism = defining property of living organisms; consciousness = defining property of the whole individual.
No, but they are remarkably similar. NCERT says the diversity of life is huge, yet the chemical composition and metabolic reactions are 'remarkably similar' across all living things. This shared metabolism is one reason it works as a universal defining feature.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. NCERT clearly states metabolism is a defining property of living organisms because every living thing has it and no non-living thing has it. This is a favourite conceptual point in NEET.
Growth also occurs in non-living things (mountains, crystals), reproduction is absent in mules and sterile organisms, and movement is not shown by all life. Only metabolism is present in all living things and absent in all non-living things, so it alone is 'defining'.
No. An isolated enzyme reaction in vitro is a chemical event, neither living nor non-living. Life is the sum total of all metabolic reactions happening together in an organised cell, not a single reaction alone.
For the whole individual, NCERT describes consciousness (the ability to sense and respond to the environment) as the defining property, while metabolism is the defining feature at the cellular/chemical level.
No. A dead body has cells and molecules, but its metabolic reactions have stopped, which is exactly why it is non-living. Metabolism, not the mere presence of cells, marks something as alive.
